Unmanned Systems Technology 020 | Alpha 800 I Additive Manufacturing focus I USVs insight I Pegasus GE70 I GuardBot I AUVSI Xponential 2018 show report I Solar Power focus I CUAV Expo Europe 2018 show report

65 design that avoids the problems with wheels or tracks that can become bogged down in mud or snow. The design is intended to allow the system to operate in a variety of conditions, from marshland and over railway tracks to snow and even on water. A spherical robotic platform has numerous advantages for missions including search and rescue, general surveillance and military robotics, from detecting explosives to video reconnaissance. In security applications, for example, the GuardBot system itself can be remotely operated or programmed to navigate or patrol a set route of waypoints along perimeters, buildings or fields autonomously. Cameras mounted on each side of the sphere can be positioned independently in order to monitor conditions or check for intruders. However, developing a propulsion system for the spherical design posed several challenges, such as developing the pendulum to minimising vibration to provide a stable platform for the cameras, which stream live video back to an operator. That means the system also has to integrate a radio comms system that supports HD video transmission, an encryption capability, mesh networking and even satellite comms so that it can operate in areas outside other wireless networks. The 60 cm (2 ft) diameter system weighs 120 kg (54 lb) and can roll at about 6 mph on land and 3 mph on water. It gets its power from a 48 V battery pack that runs for up to 25 hours in operation and 45 hours when stationary. Its two cameras are mounted in glass domes on the sides, and it can include sensors to detect radioactivity, gas and chemicals ranging from those in explosives to illegal drugs. The company has developed smaller prototypes down to 18 cm (7 in) or even 12 cm (5 in) in diameter. These can be used to roll autonomously underneath a ground vehicle to look first for any explosives or drugs, for example. The company has also developed a concept manned version that is 2.7 m (9 ft) in diameter and is designed to carry two people. Each camera can rotate a full 360 º with a gyro-stabilised pan and tilt movement of 180 º . The GuardBot can also carry audio, electro-optic and infrared sensors, radar or broadcasting equipment as part of its payload. The system’s spherical shape is produced using shells that are welded together, and the sensors are mounted on opposite sides inside transparent polycarbonate domes. The main surface is wrapped in vulcanised rubber with moulded-in studs for traction, and the entire unit is sealed and waterproofed. The external pods that house the cameras and sensors are stabilised as part of the drive system. Drive system At the heart of the GuardBot is a patented drive mechanism with two internal motorised pendulums. By changing the centre of gravity of the sphere, a driving pendulum provides forward and backward motion. The second pendulum, mounted orthogonally to the first, enables the steering to make 360 º turns. The key challenge for the spherical design is countering the high level of instability on flat ground that comes from the single-point rolling contact. This contact point causes the ball to oscillate when driven by the pendulum that shifts the centre of mass (COM) in relation to the contact point. One key element of the design is that it is stable with an open-loop control architecture. This does not use a feedback loop from the output. It means that even though oscillations can occur, after they decay the robot will settle at the desired position with the COM directly above the ground contact point. GuardBot’s engineers had to design a system that could actively dampen out the oscillations to ensure a stable platform for the cameras and sensors. The goal was to use that stability to allow the user to give a direction command to the robot and have an internal electronic controller board to drive the system. That means the operator does not have to consider changes in ground slope, compensate for rolling oscillations or worry about the acceleration limits imposed by the pendulum system, as this is all handled by the internal controller. The first step was to develop a dynamic model of a spherical robot system with the two pendulums, both of which GuardBot | Digest Unmanned Systems Technology | June/July 2018 Smaller prototypes of the system are aimed at being used autonomously underneath a ground vehicle to look for things like explosives